When someone steals something, they thieve. Your dog thieves when he puts his paws on the kitchen table and quietly grabs your cinnamon toast.
You're more likely to encounter the adjective thieving than the verb thieve, but it's a perfectly good way to say "take illegally." Your brother might think it's perfectly acceptable to thieve a few gummy bears from the candy store where he works, although the store's owner might have a different opinion. At the root of thieve is the Old English þeof, or "thief."